The History of Insect Parasitism and the Mid-Mesozoic Parasitoid Revolution

Abstract

Insect parasites and parasitoids are a major component of terrestrial food webs. For parasitoids, categorization is whether feeding activity is located inside or outside its host, if the host is immobilized or allowed to grow, and if the feeding is done by one or many conspecific or heterospecific individuals, and other features. Fossil evidence for parasitism and parasitoidism consists of taxonomic affiliation, morphology, gut contents, coprolites, tissue damage and trace fossils. Ten hemimetabolous and holometabolous orders of insects developed the parasite condition whereas seven orders of holometabolous insects evolved the parasitoid life habit. Modern terrestrial food webs are important for understanding the Mid Mesozoic Parasitoid Revolution. The MMPR began in late Early Jurassic (Phase 1), in which bottom-to-top regulation of terrestrial food webs dominated by inefficient clades of predators were replaced by top-to-bottom control by trophically more efficient parasitoid clades. The MMPR became consolidated in Phase 2 by the end of the Early Cretaceous. These clades later expanded (phases 3 and 4) as parasitoids became significant ecological elements in terrestrial food webs. Bottom-to-top food webs explained by the resource concentration hypothesis characterize pre-MMPR time. During phases 1 and 2 of MMPR (Middle Jurassic to Early Cretaceous), a shift ensued toward top-to-down food webs, explained by the trophic cascade hypothesis, exemplified by hymenopteran parasitoid clades Stephanoidea and Evanioidea. Clade-specific innovations spurring the MMPR included long, flexible ovipositors (wasps), host seeking, triungulin and planidium larvae (mantispids, beetles, twisted-wing parasites, flies), and extrudable, telescoped ovipositors (flies). After the MMPR, in phases 3 and 4 (Late Cretaceous to Recent), parasitoids increased in taxonomic diversity, becoming integrated into food webs that continue to the present day.